The present invention provides dielectric heating which eliminates the problems and provides benefits unobtainable with hot purge gas heating and with conventional heating, and with an energy savings.
In the prior art, dielectric heating (in particular, microwave heating) has been suggested for many heating processes including drying, vulcanization of rubber, detoxification of dangerous substances and polymerization of fiberglass laminates. For example, U.S. Pat. No. 3,771,234 suggests the use of microwave radiation for removing volatile polar vehicles from non-polar materials (dielectric loss factors of about 0.0001 to 0.1), specifically drying of synthetic polymers.
Conventional heating plus a purge gas flow is also used (see U.S. Pat. No. 4,011,306), but as a result of poor heat transfer this can require long regeneration times or high temperatures. German Offenlegungschrift No. 2,107,717 describes a particular circulation system for moving an activated charcoal through an adsorption reactor and then through a regeneration reactor, wherein microwave energy is applied for releasing adsorbed gases, and then the charcoal is recirculated back again through the adsorption reactor. It is inherent from such continued circulation of the charcoal adsorbent that the charcoal is readily subject to attrition and mechanical degradation. Microwave heating in the presence of an added regenerating or purge gas, such as steam, for regenerating carbon adsorbents apparently is disclosed in Japanese Kokai Nos. 76/43,394 and 76/43,395. These Kokai also reveal that only certain active carbons are receptive to microwave heating of an extent adequate for desorption and regeneration with the heat treatment history of the carbon adsorbent affecting and determining whether desorption by microwaves be operable. Japanese Kokai No. 76/145,491 concerns regenerating an activated carbon through exposure to a high frequency electrical field to remove adsorbed substances by small discharge plasma.
The prior art also includes, such as described in U.S. Pat. No. 4,038,050, an electrical desorption of molecular sieve adsorbents wherein during desorption-regeneration there is provided an electrical current flow from one electrode and then from particle to particle of the adsorbent to another electrode.
As is well known in the art, heating with microwaves provides high frequency oscillatory movement of the molecules within the material by the combined interaction of the electric and magnetic fields associated with absorbed electromagnetic energy. The rapid temperature increase of the material is caused by this molecular friction.